Suppression of corrosive action of carbonic acid



Patented May 17, 1949 SUPPRESSION OF CORROSIVE ACTION OF CARBONIC ACID Elza Q. Camp, Goose Creek, Tex, assignor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application November 2, 1945, Serial No. 626,447

2 Claims. 1

This invention is directed to a method for suppressing the corrosion of ferrous metals in the presence of carbonic acid. Specifically, it is directed to the prevention of corrosion of steel in water containing dissolved carbon dioxide.

In many operations, it is desirable to use steel equipment (valves, lines, exchanger shells, tube bundles, etc.) in the presence of water containin dissolved carbon dioxide. More specifically, it is desirable to use steel equipment in the presence of steam condensate in which is dissolved carbon dioxide and small amounts of oxygen. It is commonly known that water solutions of carbon dioxide are corrosive to steel equipment.

The afore-mentioned corrosion reaction occurs at atmospheric temperature and pressure. Higher temperatures and pressures accelerate this type of reaction.

It is, therefore, the main object of the present invention to provide a process whereby the corrosion of steel equipment in the presence of water solutions of carbon dioxide is substantially eliminated.

In accordance with the present invention, corrosion resulting from the afore-mentioned type of reactions involving carbonic acid solutions is substantially eliminated by including in the water solutions of carbon dioxide small amounts of sulfur compounds, which may be termed non-metal sulfides and may be illustrated by hydrogen sulfide, aliphatic mercaptans such as butyl mer captan, and inorganic and organic sulfides such as ammonium hydrosulfide, carbon disulfide, and the like.

The amounts of these materials employed to prevent the afore-mentioned types of corrosion reaction are small and will vary with the individual sulfur compounds. Illustrative concentrations are as follows:

Weight Per Cent, Based on Water Material Added Solution of Cab The mechanism by which these materials are effective in preventing corrosion is not understood, but it is believed to be due to the formation of a protective film on the metal. It is understood, of course, that I do not wish to bind myself to any theory offered as explanation of the beneficial effect.

An advantage of the process of the present invention, irrespective of the prevention of corrosion of ferrous metals, is the ability to use existing equipment in which ferrous metals are present in processes involving the use of water in which is dissolved carbon dioxide.

In order to illustrate the beneficial effects of this invention, carbon steel was immersed in air saturated distilled water under a pressure of 35 pounds per square inch gage of carbon dioxide. The tests were in progress for 24 hours at a temperature of F. The carbon dioxide was admitted to the system through a pressure regulator valve, thus maintaining a constant pressure of 35 pounds per square inch gage on the system and thereby maintainin the distilled water in which the carbon steel was immersed saturated with carbon dioxide at the temperature and pressure at which the tests were conducted. The carbon steel was weighed carefully prior to immersing in the aqueous solution of carbon dioxide and after the period of exposure to the solution the steel was removed from the solution, corrosion products cleaned away and the steel was reweighed. Loss in weight was calculated on the basis of penetration in inches per year since this is the common way of reporting corrosion of metals by corrosive solutions. The results obtained in these tests are shown in the following table:

It will be observed from the data presented in 0 the foregoing table that the addition of small amounts of either carbon disulfide, butyl mercaptan, ammonium hydrosulfide, or hydrogen sulfide effects marked reductions in the tendency of water solutions of carbon dioxide to corrode steel.

The nature and objects of the present invention having been fully described and illustrated, what I wish to claim as new and useful and to secure by Letters Patent is:

1. A method of reducing the corrosive action of a mixture consisting of water, air and carbon dioxide in contact with ferrous metal in steam boiler systems which comprises injecting in said system an inhibiting amount of carbon disulfide.

2. A method of reducing the corrosive action of a mixture consisting of water, air, and carbon dioxide in contact with ferrous metals which comprises maintaining in said mixture an inhibiting amount of carbon disulfide in the range between 0.1 and 2.0% by weight of the mixture.

ELZA Q. CAMP.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,075,976 Calcott Apr. 6, 1937 FOREIGN PATENTS Number Country Date 314,842 Great Britain July 11, 1929 OTHER REFERENCES 

